Permanent completion devices for cased wellbores are known to those skilled in the art, as evidenced by U.S. Pat. No. 3,706,344 to R. R. Vann. Some boreholes extend through a highly unconsolidated hydrocarbon bearing formation which causes sand to be produced therefrom along with the hydrocarbons. The continuous production of sand is undesirable because of the deleterious effects upon the downhole equipment as well as causing above ground problems with the gathering system. Reference is made to U.S. Pat. No. 4,009,757 which further discusses this problem.
In order to overcome many of the problems associated with the production of sand, those skilled in the art have employed various different techniques for "gravel packing" the pay zone. Gravel packing of a well generally includes positioning a cylindrical sand screen downhole in the borehole adjacent to the perforated zone, and straddling the perforations with packer devices so that an annular area is isolated behind the screen and between the packers. Gravel is packed into the annular area. The gravel packed zone prevents sand from flowing through the perforations and into the borehole.
In order to perforate an unconsolidated zone, and thereafter to gravel pack the zone, it has heretofore been customary to make several trips into the well. Generally, the casing is perforated with a casing gun as set forth, for example, in U.S. Pat. No. 4,140,188 and 3,717,095. The perforating gun is then removed from the borehole and a suitable gravel packing tool string run downhole and positioned adjacent to the perforations. An example of a gravel packing tool is set forth on pages 349-354 of Baker Oil Tools 1974-75 catalog; 7400 E. Slauson Ave; Los Angeles, California 90040. Gravel is flowed downhole to the tool and into the annular area between the screen and the perforations, with some of the gravel flowing back into the perforations and into the unconsolidated zone, thereby reinforcing the unconsolidated zone and preventing the production of sand therefrom, while at the same time, minute passageways are left through which the produced hydrocarbons can flow into the cased borehole.
The above operation generally is carried out after the casing has been cemented into place, and before the drilling or work-over rig is moved off location. In any event, several different trips into the borehole are required, each of which represents a considerable amount of time, cost and effort. It would therefore be desirable to be able to make a single trip into a borehole with a tool string, and to use the tool string to perforate the pay zone and subsequently gravel pack the perforated zone before coming out of the hole. Method and apparatus for completing a well in a single trip into the borehole is the subject of the present invention.